The field of the present disclosure relates generally to carbon to liquids systems and, more specifically to a Fischer-Tropsch reactor having increased carbon to liquids conversion.
The terms C5+ and “liquid hydrocarbons” are used synonymously to refer to hydrocarbons or oxygenated compounds having five (5) or greater number of carbons, including for example pentane, hexane, heptane, pentanol, and pentene, which are liquid at normal atmospheric conditions. The terms C4− and “gaseous hydrocarbons” are used synonymously to refer to hydrocarbons or oxygenated compounds having four (4) or fewer number of carbons, including for example methane, ethane, propane, butane, butanol, butene, and propene, which are gaseous at normal atmospheric conditions.
At least some known Fischer-Tropsch (FT) units in combination with steam methane reforming (SMR) units have been optimized to produce synthetic fuel (synfuel) from natural gas, also known as a Gas-to-Liquids process (GTL). Typically, natural gas refers to methane-rich gas mixture that can include carbon dioxide, nitrogen, hydrogen sulfide, and other hydrocarbons in various proportions. In at least some known GTL processes, natural gas is converted to synthesis gas (syngas) with a steam reformer for use in the FT reactor. Known steam reformers generally operate at temperatures of about 800° C., which requires pre-heating of the natural gas and steam used therein. Steam reforming is an endothermic process, and thus requires an external heat source to maintain a suitable process temperature. As such, in these known reformers a portion of the natural gas is combusted to produce the heat required for the pre-heating and reforming processes. However, using a portion of natural gas for these purposes reduces the overall cost efficiency of the GTL system.
The reaction chemistry of a FT process involves converting hydrogen and carbon monoxide to a variety of hydrocarbons and water with a catalyst. While these known catalysts activate the FT reaction, water produced during FT synthesis may decrease the conversion of carbon monoxide by deactivating the catalyst. For example, high water partial pressure may cause deactivation of the catalyst by oxidizing the active catalyst sites, while low water partial pressure may cause competitive adsorption among water, carbon monoxide, and hydrogen molecules on the catalyst active site. At least some known methods for facilitating preventing deactivation of a FT catalyst include controlling the partial pressure of water produced during FT synthesis and/or increasing the catalyst's resistance to attrition by adding a certain quantity of titanium. However, these known methods may be costly to implement and may facilitate only marginal improvements in overall carbon monoxide conversion.